How to keep shingles straight?

Keeping shingles straight during installation is essential for both appearance and waterproofing performance, as crooked courses can expose nail lines and create channels for water intrusion. Professional roofers use several techniques to ensure straight lines. First, they establish a true horizontal baseline by measuring up from the eave at both ends of the roof and snapping a chalk line across the entire roof deck. This line compensates for any slight irregularity in the eave. They then snap additional horizontal chalk lines every few courses, typically every 5 or 6 rows, to maintain alignment and prevent drift that can occur from small errors accumulating. Vertically, they use a stair-step or pyramid installation method rather than installing one full row at a time, which helps keep the pattern aligned and prevents vertical lines from wandering. Using shingles with built-in alignment notches or using the cutout slots as visual guides also helps. For DIYers, it is important to not rely on the edge of the previous shingle as the sole guide, as one crooked shingle will cause all subsequent shingles to be crooked. Regularly step back and sight down the roof from a distance to check for straightness. Keeping shingles straight also means storing them flat and not installing them in extreme heat when they can stretch or in cold when they are stiff.